|
|
Mangroves in Australia page 2
Mangrove Zones
Different mangrove species have different requirements. Some are more tolerant of salt than others. They have different nutrition needs. The plants are affected by wave energy, soil oxygen levels, and drainage. When a species finds its preferred conditions, it becomes stronger and more plentiful than others. This has led to quite clear zones among mangroves.
The zones run parallel to the shore or to the banks of tidal creeks:
Along the sea
side, there is generally an area of grey mangroves, best adapted to a wide range of soil conditions. It is a tough species, and is Australia's most common mangrove due to its ability to tolerate low temperatures and a variety of other intertidal conditions. It is generally the first to start growing on new mud banks, with its distinctive peg roots. The Mangrove apple often grows in this zone
too.
The red mangrove, also known as the stilt or spider mangrove,
is usually found behind this zone where its long prop roots anchor
it in wind and waves.
The next zone
is the part that is flooded only sometimes, at times of very high
tides. The soil is firmer but saltier because of the irregular
flooding: the water evaporates and leaves a coating of salt which
does not get diluted until the next flooding. The yellow mangrove
species are found in this zone. Conditions make it difficult
for other species to survive here, other than saltmarshes or succulent
plants.
Further zones can see the grey mangrove again, and in less salty
soil there may be a thick forest of the orange mangrove
species.
Local conditions dictate what is found on the land side. For example, in tropical areas there may be regular flooding and freshwater swamps with less salt tolerant plants. There may be a zone of paperbark swamps as vegetation merges into rainforest. In areas seasonal rainfall, evaporation could mean increased saltiness, so there may be a saltmarsh.
The richest mangrove
communities are found in tropical and sub-tropical areas where
the water temperature is over 24ºC in the warmest month,
where the annual rainfall is more than 1250mm and high mountains
are close to the coast, ensuring rainfall.
Mangroves need protection from high energy waves which erode the
shore and prevent seedlings from becoming established.
Survival
Strategies of Mangrove Plants
If you use any part of this in your own work, acknowledge this source in your bibliography like this:
Sydenham, S & Thomas, R. Mangroves in Australia. [Online]www.kidcyber.com.au (2003)
Updated ©kidcyber [2008]